<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <meta http-equiv="X-UA-Compatible" content="ie=edge" />
    <title>后盾人</title>
  </head>
  <body></body>
  <script>
    let arr = [1, 2, 3, 4, 2, "9"];
    console.log(arr.lastIndexOf(2, -3));
    // console.log(arr.indexOf(-4));
    // if (arr.indexOf(2) != -1) {
    //   console.log("找到了");
    // }
    // console.log(arr.includes(2));
    // console.log(arr.includes(399));
    // if (arr.includes(399)) {
    //   console.log("找到了");
    // }
  </script>
</html>
